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Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.

The new ECHA CHEM database has been released by ECHA, and it now contains all REACH registration data. There are more details on the transition of ECHA's published data to ECHA CHEM here.

Diss Factsheets

Physical & Chemical properties

Dissociation constant

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Administrative data

Link to relevant study record(s)

dissociation constant
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
the study does not need to be conducted because the substance is hydrolytically unstable (half-life less than 12 hours)

Description of key information

Dissociation constant [trichlorosilane]: Not relevant due to very rapid hydrolysis in contact with water

Dissociation constant [silicic acid]: pKa1 = 9.9

Key value for chemical safety assessment

Additional information

The requirement to test the substance for dissociation constant is waived because in contact with water the substance hydrolyses very rapidly to form silanetriol/monosilicic acid and hydrochloric acid.

Monosilicic acid was reported to have dissociation constant values of pKa1 = 9.9, pKa2 = 11.8, pKa3 and pKa4 = 12 at 30°C in a secondary data source which has been subject to peer review and in which the original sources are traceable. Monosilicic acid is, therefore, an extremely weak acid. In neutral solution, the undissociated form will dominate.